OK men, Today I went out to zero in a new build. Colt Sporter II big hole lower with a Colt A1 (real A1 not slick side) big hole upper I found at a gun show. I have a gap between the upper and lower (see picture) This upper has all the correct Colt markings and the big hole looks and "feels" factory.

just about every round would slam into the face of the upper receiver right below the extension. There is very little wobble to the upper and the big hole pin fits smoothly. I was using Winchester Q3131 5.56 ammo for zeroing. In order for me to fire more than one round at a time I had to hold the mag and push it forward. (new DSG black teflon mags)

I did try several different mags, Center, D&H, Adventure Line etc and all had the same issue. It seems that the gap is raising the angle of attack on the cartridge so it does not make it into the feed ramp.

Does anybody know of a way to remedy this? I would not rule out the dreaded Dremel tool in a repair method.

would you...

enlarge the hole in the upper receiver?dremel in feed ramps?call Colt and beg for help?send it to that vendor (I forgot the name) that I heard about on this site to re-do the aluminum hole in the upper (or lower).

ETA: the lowers finish is how I found it after I stripped about 4 layers of paint off of it. I did not mill off the fence.

ChrisArmchair Commandos of the World Unite!Member of the Wolf Ammo Anti-Defamation League.Who's got a Safe Queen???

I would meet up with me.... and use my SP1 large hole upper on your lower, and see if that takes care of it.... and if it does, just ditch the upper and find another one.

I dont remember seeing a lot of "real" A1 large hole uppers. I am sure they made them, but the bulk of large hole uppers are either slickside (SP1) or A2's.... with a handful of large hole flat-tops off Colt 6700's. I'd venture, given the amount of space there, and the rarity of the config - that is a hack job. Just a guess.

Do you know you can tighten up your magazine release button, which holds the magazine tighter? Push the magazine button in with a loaded round (military advice) until you can turn the long part of the magazine catch on the left side of the rifle. Screw it in (like you're tightening it) one complete turn and see if that solves your problem, if not turn it another 360 degrees, and give it another try. I've had AR's with large gaps and if I had feeding problems, this solved the problem.

One other thing, are you sure you have the correct front hinge pin in the rifle? Good luck, but try my first suggestion as it's the cheapest!

I bought My first AR (a Colt 20" A2,used) back in '88 & it had the same problem. I showed it to the Montana Air Guard Armorer & He said He'd never seen a gap like that before in all His 20+ years. I dremmel'd the pivot hole it & shimmed it to remove the gap & it became flawless for 17 years. (Very crude fix, I know)! I recently replaced the A1 upper with an A2 (small hole) & used the off-set screw (about $5.00) & it is now fixed for good. It takes Me awhile to finish things for good, sometimes. Only about 17 years or so, this time.Anybody want to buy a slightly used (10.000 rds) A1 upper with a crude oblong pivot hole?The Ol' Crew Chief

Aircraft Commander: "Well, Chief, is She ready to fly?"The Ol' Crew Chief: "Well, Loo-tennet, when Ya get down to the end of the runway&pull-back on the contol column, We'll all find-out together!"